CAMBRIDGE, Mass.—The men who appeared to be the most-recent victims of Boston's alleged bombers were praised Friday—one as a gregarious outdoorsman who embraced his campus police-officer role, the other a father and revered transit officer who took his job to heart.

Massachusetts Institute of Technology Patrol Officer Sean A. Collier, 26, was shot to death late Thursday after he was ambushed by the suspects at the start of a hectic and bloody rampage through Cambridge and Watertown, officials said.

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Officer Sean Collier
Associated Press

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Officer Richard Donohue
tAssociated Press

Later, Richard Donohue Jr., 33, an officer with the region's transit authority, was shot during an exchange of gunfire with the suspects as they were being pursued by police while they drove in a carjacked Mercedes, according to the district attorney's office in Middlesex County. Mr. Donohue was in critical but stable condition Friday following surgery at Mount Auburn Hospital, a hospital spokesman said.

"Sean was one of these guys who really looked at police work as a calling," said MIT Police Chief John DiFava, in a release. "He was born to be a police officer."

Mr. Collier, of Somerville, Mass., joined the MIT police in January 2012 and quickly became involved with students, particularly the MIT Outing Club for fans of outdoor activities, police officials said. In a little more than a year on the job, he made a big impact on campus and in the club, joining students hiking and skiing.

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"It really struck me how enthusiastic Sean was," said Matthew Gilbertson, a graduate student in mechanical engineering at MIT who said he became quick friends with Mr. Collier through the club. Within hours of his name being released by authorities, at least two online tributes had been created in his honor.

Mr. Collier cracked up students by yodeling on treks, dancing the Lindy Hop in uniform and hiking in his heavy work boots and work belt, the tributes reported. He surreptitiously led students on a mountaineering training session up 20 flights of stairs inside a Cambridge building, and his friends remembered his "irrepressible" grin and fondness for pepperoni as a hiking snack.

"I will never forget the time you showed me the view of Boston from the top of the Green building; the time you called out to me on Vassar Street using the mega phone in your police car" wrote a poster listed as Sarah. She added that she came to know him through his visits to her workplace when he was on patrol.

Photos: Chaos in Boston

This photo released by the FBI shows a suspect that officials identified as Dzhokhar Tsarnaev.
Associated Press

Another post read: "Officer Collier died a hero. I am more grateful than I have words to say that Officer Collier stood tall as a shield for us, and that his life was not given in vain. My thoughts and prayers are with his family."

Mr. Collier's younger brother Andrew is a machinist in the engine department at auto racing's Hendrick Motorsports. In a video on the Nascar website, driver Jimmie Johnson said it was "a very sad time," adding, "My thoughts and prayers are with the Collier family."

Mr. Donohue has worked for the Massachusetts Bay Transportation Authority for three years and was awarded a commendation earlier this year for saving a life, according to transit spokesman Joe Pesaturo. Mr. Donohue is married and has a six-month-old child, Mr. Pesaturo said.

"Facing extraordinary danger, Officer Donohue never hesitated in fully engaging the terrorists in order to protect the citizens of the Commonwealth," said authority Police Chief Paul MacMillan in a statement. "I am extremely proud of him, and cannot say enough about his heroic actions."

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Mr. Donohue and Mr. Collier attended the same police-training academy, said Ed Donohue, the victim's brother, who also works as a police officer in their hometown of Winchester. "I feel devastated," he said. "We're very proud of all the first responders that were on the scene."

Richard Howard, town manager at Winchester, said Mr. Donohue is a native of the town of about 22,000 eight miles outside downtown Boston. His parents, grandmother and brother still live in Winchester, where his family is "very well-known and highly regarded," said Mr. Howard.

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